Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $84.98   3.184%   $87.6858   $87.69   $87.70   $87.70  
  Purchase #2 $120.54   9.453%   $131.9346   $131.93   $131.95   $131.90  
  Purchase #3 $108.36   6.179%   $115.0556   $115.06   $115.05   $115.10  
  Purchase #4 $214.81   10.114%   $236.5359   $236.54   $236.55   $236.50  
  Purchase #5 $106.25   5.184%   $111.758   $111.76   $111.75   $111.80  
  Purchase #6 $105.50   8.594%   $114.5667   $114.57   $114.55   $114.60  
  Purchase #7 $155.61   3.212%   $160.6082   $160.61   $160.60   $160.60  
  7 purchase totals = $896.05       $958.1448   $958.16   $958.15   $958.20